Dioon argenteum sp. nov. (Zamiaceae) is described from northern Oaxaca, México. Flat leaves, and persistently tomentose, slightly imbricate leaflets with marginal prickles characterize this species. The specific epithet argen- teum was chosen to describe the silver appearance of the persistent tomentum covering the new leaves. D. argenteum appears to have affinities with D. purpusii and D. califanoi. © 2003 The Linnean Society of London, Botanical Jour- nal of the Linnean Society, 2003, 141, 471–476.
ADDITIONAL KEYWORDS: cycad – cycad species complexes – floristic refugia – Mesoamerica